1. Field of the Invention
The present invention is directed to a method of producing hydroperoxy-group-containing aluminum compounds and such compounds so produced. More specifically, the present invention is directed to a method of producing hydroperoxy-group-containing aluminum compounds in a sheet or plate-like form, the compounds being transparent, appearing polymeric in nature, and having the physical appearance of mica.
2. Description of Prior Art
The patent literature describes various types of transparent alumina and processes for producing such transparent alumina. For example, U.S. Pat. No. 3,026,210 to R. L. Coble describes a transparent alumina in which the alumina comprises high density polycrystalline alumina bodies having in-line transmission of not less than 10%/ml thickness of radiant energy of wave length in the range from 0.30 micron to about 6.6 microns. Such transparent alumina bodies are prepared by compacting a mixture of finely divided alumina with minor additions of magnesia and firing the compact for predetermined periods of time at a temperature not lower than about 1,700.degree. C., either in a vaccum or in a hydrogen environment.
U.S. Pat. No. 3,026,177 to P. D. S. St. Pierre, et al. also involves the preparation of transparent polycrystalline alumina. In accordance with this patent, the product is produced by compacting a substantially pure, finely divided alumina and subjecting the compact to a first firing in a hydrogen atmosphere at a temperature of from about 1,650.degree. C. to 1,750.degree. C. for a period of from 50 to 300 minutes and thereafter, subjecting the alumina body to a second firing in a hydrogen atmosphere at a temperature of from about 1800.degree. C. to 2000.degree. C. for a period of not less than 15 minutes. This second firing is said to improve the transparency of the polycrystalline alumina.
U.S. Pat. No. Re. 27,083 in the name of Emile A. Klinger, et al., describes a dense polycrystalline body of alumina which has adequate transparency and high mechanical strength. Such product is described as having an average size of grains of less than 10 microns and a specific gravity greater than 3.96. The polycrystalline body of fine grained alumina is obtained by compacting a powder of aluminum oxide particles having a particle size not substantially greater than 3 microns and sintering the compacted body in the substantial absence of gases having a molecular weight substantially greater than that of hydrogen for a period of 3 to 30 minutes at a temperature of 1700.degree.-1950.degree. C.
Also, U.S. Pat. No. 3,718,494 to Howard H. Jacobson describes sheet-like alpha alumina having an average thickness of 10-250 m.mu. and major faces averaging 15-1000 m.mu..sup.2. Such sheet-like alpha alumina is prepared by the formation of mullite in the presence of a reactive flouride salt such as cryolite.
With the exception of the last noted patent to Jacobson, each of the above-described processes involves compacting a high temperature sinter to produce transparent bodies of alumina. None illustrates the direct production of an aluminum-containing product, such as alumina, in a transparent form directly in its formative reaction. Furthermore, in none of these products is the alumina in a sheet-like or plate-like form, having a physical structure similar to mica and appearing polymeric in nature.
The preparation of an aluminum product having a substantial amount of hydroperoxy groups is a desirable goal in that the hydroperoxy groups create unique physical and chemical characteristics in the aluminum compound. For example, unique reactivity and catalytic properties are associated with the presence of hydroperoxy groups. The use of hydrogen peroxide to produce an alumina product, specifically as a hydro-forming catalyst, is illustrated in U.S. Pat. No. 2,852,473 to Welling.
The Welling patent relates to a process which involves a first amalgamation of aluminum with a solution of a mercuric salt, such as mercuric chloride, and subsequent contacting of the amalgamated aluminum with a dilute aqueous solution of hydrogen peroxide. With respect to the desired hardness, porosity and surface area of the catalyst, a desirable product is said to be obtained when the temperature of the reaction medium is maintained between about 70.degree. C. and the boiling point of the aqueous hydrogen peroxide. Generally, a granulated aluminum is utilized to prepare this alumina hydro-forming catalyst.
A process such as described in the Welling patent cannot produce an alumina product in which the product is transparent, in sheet or plate form and with the physical appearance of mica. Moreover, a product such as that produced by the process of Welling cannot be polymeric in nature. Still further, the hydroperoxy group content of such product is minimal due to the presence of a substantial amount of water in the reaction system and the employment of a high temperature reaction, since hydrogen peroxide is unstable under the temperature conditions of Welling. Still further, the use of a conventional amalgamated aluminum does not lend itself to the preparation of an aluminum product containing hydroperoxy groups and one which can be characterized as transparent, in sheet or plate form and with the physical appearance of mica. Such a product has now been obtained, however, by adherence to the parameters of the present invention.